Tissue Hemoglobin Monitoring Is Unable to Follow Variations of Arterial Hemoglobin During Transitions From Pulsatile to Constant Flow in Cardiac Surgery

ObjectiveTo test whether the variations of tissue hemoglobin concentration (∆THb) measured by the FORE-SIGHTTM cerebral oximeter can accurately detect changes in arterial hemoglobin concentration (∆AHb) before, during, and after cardiopulmonary bypass.DesignA prospective clinical study.SettingCardiac surgery operating room.ParticipantsThirty patients scheduled for cardiac surgery.InterventionsTissue hemoglobin concentration (THb) was recorded continuously via 2 sensors applied on the forehead and connected to the cerebral oximeter. Arterial hemoglobin concentration (AHb) was measured in a hematology analyzer laboratory. Hemodynamic and respiratory parameters as well as epidemiologic data also were noted. Data were collected at 3 perioperative times: After induction of anesthesia, 10 minutes after cardioplegia, and at the end of the surgery.Measurements and Main ResultsNinety pairs of data were collected. The coefficient of linear regression between ∆THb and ∆AHb was 0.4 (p<0.001). After exclusion of Hb variations<5%, the trending ability of THb to predict ∆AHb was 87%. However, the Bland and Altman plot graph for THb and AHb showed major limits of agreement (2.4 times the standard deviation). Central venous pressure and carbon dioxide tension were linked independently and positively with THb (p = 0.03).ConclusionsContinuous monitoring of THb cannot accurately track variations of AHb during the transition from pulsatile to continuous flow and vice versa in cardiac surgery. Local hemodynamic factors such as PaCO2 and vasodilation significantly impact THb. In this setting, THb monitoring should not be used to guide eventual blood transfusion management.